Support stream inheritance for the forked process

[gnodet]

Related to a jline issue.
Java 7 introduced the ability to inherit standard streams using the inheritIO() method.
It would be really nice to be able to support it.

[gnodet]

@olamy, would you mind having a look at this PR if you have a few minutes ?

[olamy]

@gnodet LGTM please do a real pr. ATM it's only a change in your fork :-)

[gnodet]

@olamy The related PR is #72

[khmarbaise]

It would be great having an unit or integration test for this?

[gnodet]

Fair enough, I'll have a look.

[gnodet]

I wrote an integration test, but unfortunately, I don't see a good way to make it work.
The reason is that the way I thought about testing that is to run the tty unix command which returns the name of the terminal device. If the inheritIo flag works, it should be an existing terminal, else the command returns not a tty. The problem is that this can only work if the maven process actually has a terminal correctly set up (that's the exact problem I'm trying to solve for the exec'ed process here). So in order for that to work, it would require the maven-invoker-plugin to also be able to inherit the terminal. Furthermore, this would also only work if running from a real terminal, so that automated testing in jenkins or such may not work.